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Dr. Kent Brantly, with North Carolina-based Samaritan’s Purse, arrived in Atlanta for treatment Saturday. Brantly was a resident at JPS Hospital in Fort Worth before he went to Liberia. Both he and Writebol contracted Ebola while treating patients in Liberia.

A spokeswoman for Brantly’s employer, Samaritan’s Purse, said Monday evening that he no longer wants his condition and treatment shared, for his privacy. But earlier reports indicated he also was improving.

Ebola has killed at least 887 people in four West African countries in what’s considered one of the largest outbreaks ever.

Both Americans received an experimental serum, and both are improving, although it’s impossible to know whether the treatment is the reason or they are recovering on their own.

ZMapp

The experimental treatment the U.S. aid workers are getting is called ZMapp and is made by Mapp Biopharmaceutical of San Diego. It is aimed at boosting the immune system’s efforts to fight off Ebola and comes from the Nicotiana plant, according to a statement on Mapp’s website, www.mappbio.com.

In a statement, the company said it was working with LeafBio of San Diego, Defyrus Inc. of Toronto, the U.S. government and the Public Health Agency of Canada on development of the drug, identified as a possible treatment in January.

The statement says they are “cooperating with appropriate government agencies to increase production as quickly as possible,” but gives no details on who else might receive it or when.

The U.S. Food and Drug Administration must grant permission to use experimental treatments in the United States, but the FDA does not have authority over the use of such a drug in other countries. The aid workers were first treated in Liberia. An FDA spokeswoman said she could not confirm or deny whether the FDA granted access to any experimental therapy for the aid workers while in the U.S.

Writebol, 59, received two doses of the experimental treatment while in Liberia. Johnson was hesitant to credit the treatment for her improvement.

“Ebola is a tricky virus, and one day you can be up and the next day down. One day is not indicative of the outcome,” he said. But “we’re grateful this medicine was available.”

Brantly, 33, also received a unit of blood from a 14-year-old boy, an Ebola survivor, who had been under his care.

Samaritan’s Purse initiated the events that led to the two workers getting ZMapp, according to a statement Monday by the National Institute of Allergy and Infectious Diseases, part of the U.S. National Institutes of Health. The charity, based in Boone, N.C., contacted U.S. Centers for Disease Control and Prevention officials in Liberia to discuss experimental treatments and were referred to an NIH scientist in Liberia.

The scientist answered some questions and referred them to the companies but was not officially representing the NIH and had no “official role in procuring, transporting, approving, or administering the experimental products,” the statement says.

The Defense Department has long had a hand in researching infectious diseases, including Ebola. During much of the Cold War period, this served two purposes: to keep abreast of diseases that could limit the effectiveness of troops deployed abroad and to be prepared if biological agents were used as weapons.

In Fort Worth, where Brantly attended Southside Church of Christ while working at JPS Hospital, members of the church gathered Sunday and prayed for him, Writebol and the people of West Africa. More than 30 members of the Liberian Community Association of Dallas-Fort Worth attended the Sunday morning service.

Southside, on Hemphill Street south of the Medical District, also collected more than $20,000 for Brantly’s family and for Samaritan’s Purse.

Staff writers Lee Williams and Sarah Bahari contributed to this report, which contains material from The Associated Press.